This chapter elaborates a model for understanding science teachers' approaches and practices with respect to Inquiry Based Science Teaching and Learning (IBST/L). This model may help teachers and other science education actors -especially teacher educators- to appreciate what IBST/L actually is, and to situate their activities within a framework encompassing the complexity of their activities. This model results from two issues arising from the 3-year S-TEAM experience. Firstly, there is a contradiction between demands for IBST/L implementation across Europe, as answered by S-TEAM, and the implications of IBST/L for teacher activities. In France, for instance, one problem is that there are many definitions of IBST/L, and we know from S-TEAM that other countries have their own interpretations.